Elucidating the impact of point defects on the structural, electronic, and mechanical behaviour of chromium nitride

TL;DR

This study uses density functional theory to explore how point defects and impurities affect the structural, electronic, magnetic, and mechanical properties of chromium nitride and its nitrogen-rich analogue CrN2, revealing defect sensitivity and implications for coatings.

Contribution

It provides new atomic-scale insights into defect effects on CrN2's properties, contrasting with CrN, and highlights defect chemistry's role in mechanical performance.

Findings

CrN2 is highly sensitive to defects, affecting electronic and mechanical properties.

CrN's metallic nature screens defects, maintaining its integrity.

Hydrogen causes anisotropic distortions; oxygen increases hardness.

Abstract

Defect engineering offers an important route to property tuning of nanostructured coatings for advanced applications. Transition metal nitrides, such as CrN, are widely used for their mechanical resilience, but their nitrogen-rich analogue CrN2 remains poorly understood, especially at the atomic scale. This study employs density functional theory to investigate the energetics as well as how intrinsic defects (vacancies, interstitials, and anti-sites) and extrinsic impurities (hydrogen and oxygen) influence the structural, electronic, magnetic, and mechanical response of CrN2, in comparison to the more commonly studied CrN. With directional N-N bonding and semiconducting character, CrN2 shows high sensitivity to defect incorporation, including local spin polarisation, gap states, and mechanical softening. In contrast, CrN's metallic character enables effective screening of similar defects, preserving its structural, magnetic, electronic and mechanical integrity. However, hydrogen induces anisotropic distortions and mechanical degradation in CrN, while oxygen enhances hardness. These findings reveal how defect chemistry and bonding anisotropy govern mechanical performance, with implications for nanoscale control in coatings design.